This invention relates to fuel injection control for starting up an internal combustion engine.
Tokkai 2000-45841 published by the Japanese Patent Office in 2000 discloses simultaneous fuel injection for all cylinders of an engine immediately after the ignition switch is switched to the ON position.
In a spark-ignition engine injecting fuel sequentially into the intake port, fuel injected during cranking of the engine adheres to the wall surface of the intake port and tends to form a flow along the wall. This phenomenon is hereafter referred to as xe2x80x9cwall flowxe2x80x9d. Consequently time is required for fuel to reach the combustion chamber and preferred stability of combustion during cranking of the engine can not be obtained. The prior-art technique aims to form a wall flow in advance as a result of injecting fuel all at once to all cylinders immediately after the ignition switch is turned to the ON position. As a result, fuel injected sequentially to respective cylinders thereafter flows into the combustion chamber smoothly without adhering to the wall face of the intake port.
Spark ignition of the air-fuel mixture in each cylinder is generally performed in the vicinity of the compression dead center. However, it is noted that each cylinder performs respectively different strokes when simultaneous injection to all cylinders is performed. Furthermore in the period after simultaneous injection to all cylinders until initial spark ignition to each cylinder, some cylinders undergo sequential fuel injection while others do not undergo sequential fuel injection.
As a result, a deviation is produced in the air-fuel ratio of the fuel mixture at initial sparking ignition in each cylinder. In cylinders having a lean air-fuel ratio, misfiring may result. In cylinders having a rich air-fuel ratio, incomplete combustion may result. Both misfiring or incomplete combustion have an adverse effect on the stability of the engine and on the exhaust emission components.
It is therefore an object of this invention to increase stability of combustion in each cylinder when starting an engine which performs sequential fuel injection.
In order to achieve the above object, this invention provides a fuel injection control device for an internal combustion engine that is provided with a plurality of cylinders which sequentially perform a combustion of fuel and a starter motor which cranks up the engine.
Each of the cylinders has an intake port and a fuel injector which injects fuel into the intake port, and sequentially performs an intake stroke, a compression stroke, an expansion stroke and an exhaust stroke.
The control device comprises a first sensor which detects a start of the starter motor, a second sensor which detects a specific position in a specific stroke of each cylinder and generates a corresponding signal, a third sensor which detects a temperature of the engine, and a programmable controller.
The controller is programmed to determine if the temperature is lower than a predetermined temperature, execute a cylinder-stroke identification identifying a present stroke of each cylinder based on the signal generated by the second sensor, control the fuel injectors to perform a preliminary fuel injection for all the cylinders when the temperature is lower than the predetermined temperature, during a period between the start of the starter motor and a first execution of the cylinder-stroke identification, and control the fuel injectors to perform a primary fuel injection for a cylinder in the exhaust stroke and for a cylinder in the intake stroke simultaneously, on the first execution of the cylinder-stroke identification.
This invention also provides a fuel injection control method for the above described internal combustion engine. The method comprises detecting a start of the starter motor, detecting a specific position in a specific stroke of each cylinder and generating a corresponding signal, detecting a temperature of the engine, determining if the temperature is lower than a predetermined temperature, executing a cylinder-stroke identification identifying a present stroke of each cylinder based on the signal, controlling the fuel injectors to perform a preliminary fuel injection for all the cylinders when the temperature is lower than the predetermined temperature, during a period between the start of the starter motor and a first execution of the cylinder-stroke identification, and controlling the fuel injectors to perform a primary fuel injection for a cylinder in the exhaust stroke and for a cylinder in the intake stroke simultaneously, on the first execution of the cylinder-stroke identification.
The details as well as other features and advantages of this invention are set forth in the remainder of the specification and are shown in the accompanying drawings.